In recent years, research and development has been actively made on functional materials of organic compound. Recently, the development of an organic electroluminescence device (organic EL device) employing an organic compound as a material for constituting a light emitting device is promoted actively.
An organic electroluminescence device has a structure wherein a thin film comprising a light emitting organic compound is interposed between an anode and a cathode. The electrons and the holes each injected into the thin film recombine to generate excitons. The organic electroluminescence device emits light which is released from the excitons when deactivated. An organic electroluminescence device is capable of emitting light in response to a direct current at a voltage as low as about several volts to tens of volts and emitting light with various colors, for example, red, blue and green, by changing the kind of light emitting organic compound to be used. With these characteristics, an organic electroluminescence device is expected to be applied to various light emitting devices, display devices, etc.
The thin film with a thickness of 1 μm or less which includes a low molecular weight compound as a light emitting organic compound is generally formed by a vacuum vapor deposition method. However, a vacuum vapor deposition method requires an expensive vapor deposition apparatus, in addition, its production efficiency is not high and a large-sized substrate is difficult to use in some cases. An organic electroluminescence device employing only a low molecular weight compound may be poor in the mechanical strength and the heat stability of the thin film. Recently, the development of an organic electroluminescence device employing a light emitting conjugated polymer as the light emitting organic compound (polymer organic electroluminescence device) has been actively promoted, because a polymer enables the patterning by a printing method and is advantageous as a material for producing a large-sized TV panel and a flexible sheet display.
The inventors have developed and proposed a new polymer compound having a thiophene derivative in the polymer backbone (for example, Patent Document 1). Many studies have been made on polymer organic electroluminescence devices because of their advantages of capable of forming films by a coating or printing method (Patent Documents 2 to 4). However, as compared with an organic electroluminescence device employing a low molecular weight compound, the emission efficiency of a polymer organic electroluminescence device is low. In addition, it has been required to further improve the efficiency and lifetime of an organic electroluminescence device employing a polymer.